Abstract

Results are presented for the first imaging system that combines the high power of terahertz quantum cascade lasers with three-dimensional image reconstruction based on filtered back-projection. Images of various phantoms have been successfully reconstructed revealing both their external and internal structures.

Figures (6)

(a) Data acquisition methodology – A series of parallel beams are passed through the sample in the plane to be imaged and the intensity of the transmitted beams are detected, forming a 1D absorption projection. The sample is then rotated by an angle θ and the process is repeated. This process continues until data have been collected over an angular range of 180°. (b) Experimental apparatus for undertaking imaging with a THz QCL.

Photographs (a-c) and reconstructed images (d-f) of an expanded polystyrene phantom with: (a,d) a triangular cross-section and containing a cylindrical hole, (b,e) a square cross-section and containing a hole of elliptical cross-section, (c,f) a circular cross-section and a needle of diameter 0.813 mm inserted into it. The measurement (data integration) time was 20 minutes per image. The color scales in the reconstructed images correspond to values of the absorption coefficient.

Visualisation of the reconstructed 3D image – (a) The hole inside the phantom is revealed, (b) the shape of the phantom is reconstructed, (c) the top view shows the nose and cheek features. The data integration time was 15 minutes per image slice.

Photographs (a,c) and reconstructed images (b,d) of a cylindrical phantom of: (a,b) polystyrene, and (c,d) PTFE. The reconstructed image of the cross-section of the PTFE cylindrical phantom shows the erroneous presence of a hole. This is a result of the relatively high refractive index of PTFE. The acquisition conditions are the same as for the images shown in Fig. 3.